The present invention relates generally to wireless networks and more particularly to a system and method for a high density wireless local area network.
The popularity of wireless devices is leading to increased user density within wireless local area networks operating in accordance with the Institute of Electrical and Electronics Engineers (IEEE) 802.11a/b/g standards. However, as more users are added to a given network, the available throughput per user decreases. This is due to the fact that all of the communicated data passes through access points comprising the network, and each access point is limited in data throughput capability.
One approach to increasing throughput, thereby providing for additional users, is to add more access points to the network. This approach is valid provided there are enough carrier frequencies for all of the access points to operate on a different frequency. However, this approach fails when there are no longer any unused carrier frequencies available and carrier frequencies are reused.
For example, if an access point is added on a carrier frequency that is already assigned to another access point, two “cells” operating on the same frequency results. As used herein, the term “cell” describes a single access point and the client devices associated with that access point. Moreover, the additional access point provides no additional throughput if the two cells are in close proximity and the respective service areas of the two access points overlap. No additional throughput results because the carrier sense multiple access (CSMA) mechanism typically used to mitigate interference for IEEE 802.11 products prevents the two co-channel access points from operating simultaneously.
Despite the carrier sense multiple access mechanism preventing the two co-channel access points from operating simultaneously, in many instances there is adequate signal-to-interference ratio (SIR) to allow simultaneous transmission. As used herein, the signal-to-interference ratio is the ratio of the intended signal power to the total interference signal power originating from other cells. Therefore, it is often desirable to reduce the service areas of access points such that the service areas of co-channel access points do not overlap, thereby increasing throughput.
One approach to reducing the service area of an access point is to reduce or limit the output power of the access point. This approach addresses the problem of overlapping service areas, but also decreases client received signal strength within the service area rates and consequently decreases the signal to noise ratio. Furthermore, since higher data rates require higher received signal strength than lower data rates, the usable range for higher data rates is less than the usable range for lower data rates. Therefore, reducing the output power of access points such that services areas of the cells do not overlap allows co-channel cells to simultaneously transmit, but also reduces the range for higher data rates within the intended service areas. Therefore, controlling cell size by reducing output power also results in limited throughput, resulting in breaches in the total coverage area, e.g., between the access points, for the higher data rates.
Thus, there exists a need for a system and method for a high density wireless local area network that controls cell size in a way that allows multiple cells on the same carrier frequency to transmit simultaneously, but without reducing the transmit power, thereby preserving the range capability of the higher data rates.